Break through to the portal? And that early in the game... Well, he joined Pikemen there, and Gargoyles... plus the Castle's Swordmen and Pikemen bonus, and Genies. You'll take down the Paladins, but what then? Dragons, Phoenixes... And which computer-controlled Castle should you capture first?
Honestly, I didn't go through the portal. I sailed! :)
I immediately dismissed the option of sailing:
it takes too long to build it yourself (you need to capture a third town + 8000 gold and 50 wood), and you might have to wait a long time for the computer to do it...